Latch attachment for an electromagnetically operated switching device

ABSTRACT

A latch attachment for an electromagnetically operated switching device such as a relay or a contactor. The attachment includes an adjustment means which will automatically cause a latching surface on a plunger to be engaged by a latching surface on a latch lever when the contacts of the relay are moved to their operated position by a manual force applied on the plunger.

O United States Patent 1 [111 3,882,435 Grass et al. 1 May 6, 1975 [54] LATCH ATTACHMENT FOR AN 3,238,329 3/1966 Russo 335/132 ELECTROMAGNETICALLY OPERATED EllenbertgerI ruzlce SWITCHING DEVICE 3,812,440 5/1974 Cook 335/167 [75] Inventors: William E. Grass, Milwaukee;

Walter Karch Grafton both of Primary ExaminerHar0ld Broome Attorney, Agent, or Firm-William H. Schmeling; [73] Assignee: Square D Company, Park Ridge, Ill. Harold Rathbun [22] Filed: June 28, 1974 [21] Appl. No.2 484,058 [57] ABSTRACT A latch attachment for an electromagnetically operated switching device such as a relay or a contactor. if 335/164 i i g The attachment includes an adjustment means which i f will automatically cause a latching surface on a 1 0 'g'i'' 6 plunger to be engaged by a latching surface on a latch lever when the contacts of the relay are moved to their operated position by a manual force applied on [56] References Cited the plunger.

UNITED STATES PATENTS 2,343,548 3 1944 Graves, Jr. 335/168 Clam, 8 Drawmg Flgures I02 I08 6 4 I59 I76 72 46 82 i |5Q 66 5 60 76 l 62 34 86 8 I80 I48 '24 4o 98 I52 40 I l 6 92 I26 I22 I l 3 l 38 as 64 58 i l 28 52 I l 76 I8 28 I84 24 I I 1 LATCH ATTACHMENT FOR AN ELECTROMAGNETICALLY OPERATED SWITCHING DEVICE This invention relates to electromagnetic devices and more particularly to an electromagnetic or manually releasable latch attachment that is adapted to be attached to an electromagnetically operated switching device for latching the movable parts of the switching device in an energized position after the switching device is de-energized.

Mechanically held contactors. relays and the like. are electromechanical devices which provide a safe and convenient means for switching circuits where requirements demand continuity of a circuit or absolute quietness of operation. Circuit continuity during power failures is often important in automatic processing to insure that a sequence of operation will continue from the point of interruption when power is resumed. Absolute quietness of operation is required when it is necessary for a contactor to operate in hospitals, schools or office buildings and the slight hum. characteristic of A.C. magnetic devices, is objectionable.

Convcntionally, relays, contactors and the like are furnished as basic switching units and when a mechanically held function is required. a latch attachment is secured to the basic switching unit to maintain the contacts in one condition (e.g., either open or closed). when the operating coil of the basic switching unit is dc-energized. Devices. such as relays and contactors. as well as latching attachments for the devices. are manufactured in large quantities and have individual operating characteristics because of the tolerance variations of the parts used to assemble the devices. As latching attachments conventionally are designed and manufactured to be applied as an attachment to a device. attachments usually are provided with an adjustment which will permit the operating characteristics of the attachment to be varied so the operation of the attachment is compatible with the operating characteristics of the device to which it is attached. ln devices heretofore known, many of the operating components, such as the magnets. contact carriers and the like. are externally visible and can be manually operated to simulate the position of the parts of the device when the device is energized. The adjustment for the prior art attachments usually includes a threaded member which when properly adjusted will cause the latching components of the attachment to be in a latching position when the device associated therewith was in its energized condition. The latching attachment according to the present invention is intended to be used with a device that has no externally visible or accessible moving parts so that the components of the device cannot be manually moved to their energized positions when the attachment is secured on the device. The attachment includes an adjustable means which will automatically cause the characteristics of the latch attachment to be compatible to the device to which it is attached when a manual force applied to a latching plunger in the attachment causes the contacts of the device to move to their energized positions.

It is an object of the present invention to provide an improved adjusting mechanism in a latch attachment for an electromagnetically operated switching device.

Another object is to provide a latch attachment for an electromagnetically operated switching device with a means which will automatically cause the operating characteristics of the attachment to be compatible with the operating characteristics of the device when the attachment is secured to the device and a manual force applied to a movable plunger of the attachment causes the operating member of the device to move to its operated position.

An additional object is to provide a latch attachment for an electromagnetically operated device with a releasable means which will cause the operating length of a plunger in the attachment to be automatically adjusted to be compatible with the operating movement of a plunger in the device when the attachment is secured to the device and a manual force applied to the plunger in the attachment causes the plunger in the device to move to its operated position.

Further objects and features of the invention will be readily apparent to those skilled in the art from the following specification and from the appended drawing illustrating a preferred embodiment, in which:

HO. 1 is a perspective view ofa latch attachment according to the present invention attached to a front side of a relay.

FlG. 2 is a cross-sectional view of the attachment and a portion of the relay in FIG. 1 taken substantially along lines 22 in FIG. 1.

FlG. 3 is a view of the latch member as detached from the latch attachment in FIG. 2.

FIG. 4 is a view of the left side of the member in HQ. 3.

FIG. 5 is a view partly in cross section illustrating the plunger assembly as used in the latch attachment in H6. 2.

FlG. 6 is a front plan view of the latch attachment in H0. 2 with a cover and the plunger assembly removed from the attachment. and

FIGS. 7 and 8 are views taken along the lines 77 and 88 in FIG. 6. respectively.

Referring to HO. 1 of the drawings. a basic electromagnetically operated switching device 10 includes a housing 12 having a rear end carrying a mounting plate 14 securable by suitable screws to a mounting panel. not shown. The illustrated switching device 10 is preferably of the type fully disclosed in US. application for patent. Ser. No. 412.055. which was filed by the inventors Walter C. Karch, Kenneth J. Marien and Robert C. Mierendorf on Nov. 1, 1973.

As disclosed in the Karch et al application. the housing 12 basically includes three sections l6, l8 and 20, and a cover 22. The section 16 includes an electromagnet which when energized causes the operating components, such as levers and plungers of the device 10, to move to their operated positions. The section 18 includes translating levers which are operated by the electromagnet in section 16. The section 20 is provided with a plurality of switches which are operated by the translating levers within section 18. The switches within section 20 are maintained in suitable compartments within section 20 by the cover 22 which is secured to the front end of the section 20. The section 20 also includes a movable operator 24, most clearly shown in FlG. 2. The operator 24 is linearly movable in a passage extending through section 20 and includes a front end 26 that extends into an opening 28 in the cover 22 and the rear end 30 that is engaged by operating plungers, not shown. included within the section 18. The operator 24 is biased by a spring 32 so that the operator 24 moves rearwardly when the electromagnet within section 16 is energized.

The latching attachment 34, according to the present invention. includes a housing 36 having a rear end which is positioned on the front end of the cover 22. The housing 36 includes a pair of cars 39 having passages receiving screws 40 that extend through openings in the cover 22 and are threaded into threaded ends of screws 42 that secure the section 22 to the section 18. The housing 36 has a front end closed by a cover 44 and includes a closed interior wherein an electromagnet assembly 46. a latch lever 48, a latching assembly and a pair of springs 52 and 54 are included.

The electromagnet assembly 46 includes a coil assembly 56, an armature 58, a stationary magnet pole assembly and a spring 62. The coil assembly 56 includes a molded bobbin 64 that has a cylindrical passageway 66 extending therethrough. a portion 68 integral with the bobbin 64 that provides a support for a pair of wire connecting terminals 70 and a coil winding 72 wound on the bobbin 64. The coil winding 72 has its opposite ends connected to the terminals 70.

The stationary magnet pole assembly 60 includes a U-shaped magnet iron member 74, a wave washer spring 75, a cylindrical magnet pole 76. a plate-like member 78 and an armature guide 80. The magnet iron member 74 is positioned in the interior of the housing 36 by the spring 75 and suitable abutments located in the interior walls of housing 36. The cylindrical magnet pole 76 is secured to the bight portion of the member 74 and extends into the passageway 66. The magnet iron plate-like member 78 is secured and extends between the free ends on the arms of the member 74 and has a central opening 82 aligned with the passageway 66. The armature guide 80 is formed of nonmagnetic metal to have a cylindrical shape and is secured in the opening 82 to extend in the passageway 66 and present a stop surface 84 at the right end of the passageway 66 when the attachment is viewed as in FIG. 2.

The armature 58 is formed of magnet iron to have a cylindrical shaped body 85. The body 85 has a flat left end 86 wherein an annular groove is formed to receive an annular nonmagnetic metal shading coil 88. The body 85 is guided for movement in the passageway 66 by the armature guide 80 and includes an annular surface 90 that is engageable with the stop surface 84 to limit the movement of the body 85 to the right in FIG. 2. The magnet pole 76 has a flat surface 92 confronting the end 86. The spring 62 is positioned in aligned recesses in the flat surface 92 and the end 86 to constantly bias the armature 58 to the right in FIG. to a position where the surface 90 engages the stop surface 84. The right end of the body 85 extends through the opening 82 and is reduced to provide a mushroom shaped portion that includes a headed end portion 94 that is connected to a flat right front end 96 of the body 85 by a stem 98.

The latch lever 48 includes a pivot portion 100, a handle portion 102, and a latching portion 104. The pivot portion 100 is located between the handle portion 102 and the latching portion 104 and has cylindrical bearing portions 106 at its opposite ends which are received in a pair of spaced downwardly facing open sided U-shaped sockets 108 extending from the rear side of the cover 44. The bearing portions 106 are maintained in the sockets 108, which act as journals for the bearing portions 106, by the spring 54. The spring 54 is U-shaped and preferably formed of music wire to have its bight portion received-in a groove 110 in the rear face of the cover 44 and free ends on its arm portions 112 received in V-shaped downwardly facing notches 114 on the bearing portions 106. The arms 112 have midportions positioned on suitably forward facing abutments formed on the inner walls of the housing 36 so that the free ends on the arms 112 constantly urge the bearing portions 106 into their associated sockets 108. The handle portion 102 extends from the pivot portion 100 through an opening 116 in the cover 44 so as to be externally accessible. The latching portion 104 extends rearwardly from the pivot portion 100 to present a latching surface 118 that is spaced a predetermined distance forwardly of a front surface 120. The front surface 120 is formed on a ledge 122 that extends into the interior of the housing 36 from a wall 124 of the housing 36. The ledge 122 includes a bore 126 that is aligned with the operator 24 and a counterbore 128 that surrounds the front end of the bore 126. A keyhole shaped opening. located intermediate the pivot portion 100 and the latch surface 118, includes a circular opening 130 having a diameter greater than the headed end 94 and a slot-like opening 132 having a width sized to receive the stem 98 so the latch portion 104 is held captive between the headed end 94 and the end 96 after the headed end 94 is inserted through the circular opening 130.

The rear end of the portion 104 has a seat 134 for positioning one end of the spring 52. The spring 52, which has its other end positioned on the bobbin 64, constantly urges the latch lever 48 in a counterclockwise direction about its pivot portion 100. if desired, the latch portion 104 may be provided with a pair of spaced projections 135 which engage the front edge of member 78 to prevent the latch lever 48 from being dislodged from its position within the housing when the attachment 34 is detached from the device 10.

The latch assembly 50 includes a latch member 136, a plunger 138, an adjustment means 140, a spring 142 and a release element 144. The latch member 136 basically is U-shaped and has a bight portion 146 at its rear end, a pair of spaced parallel arms 148 extending forwardly from the bight portion 146 and an arcuate web 150 extending between the free ends of arms 148 to minimize the flexure of arms 148. The arms 148 are received in suitable grooves 151 formed on opposite sides and extending forwardly of the ledge 122 to provide guides for the movement of the latch assembly 50 within the housing 36. A latch surface 152 projects outwardly from the bight portion 146 and is located to be engaged by the latch surface 118 when the rear side of the bight portion 146 is positioned on the front surface 120.

The plunger 138, in the embodiment shown. has a metal shaft 154 at its rear end and an insulating operator 156 at its front end. The front end of the shaft 154 extends with a press fit into a bore extending from the rear end ofthe operator 156. A front end 157 of the operator 156 is reduced to provide a portion having a rectangular cross section which is slidable in a rectangular opening 159 in the cover 44 so the front end 157 of the operator 156 extends externally of the front surface of the cover 44 while the rear end 158 of the shaft 154 engages the front end 26 of the operator 24.

The adjustment means acts as a constraining means and prevents relative movement between the plunger 138 and the latch member 136 when the plunger 138 moves in response to movement of the operator 24 and permits a relative movement between the plunger 138 and latch member 136 when a manual force applied to the front end 157 of the operator 156 causes the plunger 138 to move rearwardly and the operator 24 to move to a position wherein the movable components of the device are at their energized positions.

The adjustment means 140 includes a bushing 160, a retainer 162, a nut 164, a spring 166 and a constraining member 168 which are positioned on the bight portion 146. The bushing 160 extends through a suitable opening in the bight portion 146 and includes a bore which receives the shaft 154 so a portion of the shaft 154 providing the end 158 extends rearwardly of the bight portion 146 and a portion of the shaft 158 extends forwardly of the bight portion 146 between the arms 148. The retainer 162 is L-shaped and has a base 170 positioned on the front side of the bight portion 146 and an opening receiving the bushing 160. The retainer 162 has an arm portion 172 extending forwardly along an edge of the base portion 170 with a slot in the arm portion 172 extending parallel and spaced from the base portion 170. The retainer 162 is positioned on the bight portion 146 when the nut 164 is tightened on the front end of the bushing 160. The constraining member 168 is formed as a stiff metal part and has a washer-like shape with an opening 173 extending therethrough to receive the shaft 154 with clearance when an ear portion 174 is received in the slot in the arm portion 172.

The spring 166 surrounds the shaft 154 and is positioned between the nut 164 and the rear surface of the constraining member 168. As the opening 173 in the constraining member 168 which receives the shaft 154 has a diameter greater than the diameter of the shaft 154. the spring 166 causes the constraining member 168 to rotate about the pivot provided by the ear 174 and the slot in the arm portion 172 to a position wherein the edges ofthe opening 173 tightly engage the surface of the shaft 154 to prevent relative movement between the shaft 154 and the latch member 136 in a direction which would cause the shaft 154 to move in a direction that is relatively forward of the latch member 136.

The release element 144 is formed as a sleeve-like part to have a closed from end 176 with a rectangular opening 178 therein which receives the front end 157 of operator 156. The element 144 also has a rearwardly extending semicircular skirt which presents an edge 180 at the rear end of the element 144. The operator 156 is received within the sleeve-like element 144 and the spring 142, which surrounds the operator 156 and is positioned between the end 176 and the front surface of the constraining member 168, constantly urges the end 176 into engagement with the rear surface of the cover 44 and the latch assembly 50 rearwardly in the housing 36 to maintain an engagement between the rear end 158 of the plunger 138 and the front end 26 of the operator 24.

Prior to the installation of the latch attachment 34 on the front side of the relay 10. the operating distance between the rear end 158 of the plunger 138 and the latch surface 152 on the latch member 136 is adjusted manually by applying a force on the end 158 in a direction which causes the latch assembly 50 to move toward the cover 44 against the force of the spring 142 to a position where the edge 180 engages a front surface portion 182 on the constraining member 168. A continued application of the manual force will cause the constraining member 168 to rotate about its ear 174 to a position where the member 168 is more perpendicular to the shaft 154 and the edges of the opening 173 move out of engagement with surface portions of the shaft 154 so the plunger 138 moves to decrease the distance between the end 158 and the latch surface 152.

The operator 24, when the device 10 is de-energized. will be positioned by spring biased levers in section 18 forwardly to a position where a stop 184 on the operator 24 engages a stop 186 on the cover 22. The latch attachment 34 is secured to the front side of the cover 22 by tightening the pair of screws 40 into the pair of screws 42 after the latching components of the attachment 34 are released by applying a manual force on the handle portion 102 which causes the latch portion 104 to rotate clockwise in FIG. 2 to a position where the latch surface 118 is out of line of engagement with the latch surface 152. The Spring 142 is selected so the force it exerts to urge the latch assembly 50 toward the operator 24 is less than the forces exerted by the springs within the device 10 which urge the operator 24 toward the plunger 138. Thus when the attachment 34 is initially installed on the front side of the device 10, the latching components in the attachment 34 will be released and the components of the device 10 will be at their de-energized positions.

The operating characteristics of the attachment 34 are automatically adjusted to conform to the characteristics of the device 10 by applying a manual force on the front end 157 in a rearwardly direction which initially causes the bight portion 146 to engage the front surface which positions the rear end of the bushing in the counterbore 128 and the latch surface 152 in a position where it is engaged by the latch surface 118 as the spring 52 causes the latch lever 48 to rotate counterclockwise. The automatic adjustment of the characteristics of the attachment 34 is completed when a continued application of manual force on the end 157 causes the shaft 154 to move without appreciable hinderance in the opening 173 to increase the distance between end 158 and the latching surface 152. The adjustment is completed when the manual force applied to the plunger 138 causes the operator 24 to move to a position where the components of the device 10 are at their fully energized positions where they are maintained after the manual force on the end 157 of the plunger is released. After the manual force is released. the constraining member 168 prevents the shaft 154 from moving in a forward direction relative to the latch member 136. When the foregoing adjustment is completed. the device 10 will be maintained in its energized condition by the attachment 34. The release of the attachment 34 may be accomplished by a manual force applied to the handle portion 102 which causes the latch surface 118 to move out of engagement with the latch surface 152 so the operator 24 and the latch assembly 50 may move forwardly and position the components of the attachment 34 and the device 10 in their unlatched and de-energized conditions respectively, as previously described. Alternately. the attachment 34 may be released by energizing the electromagnetic assembly 46 which causes the armature 58 to move to the left in FIG. 2 and the latch lever 48 to rotate clockwise to release the engagement between the latch surfaces 118 and 152 which will cause the attachment 34 to be released and the components of the device to be in their de-energized positions as described.

While certain preferred embodiments of the invention have been specifically disclosed. it is understood that the invention is not limited thereto. as many variations will be readily apparent to those skilled in the art and the invention is to be given its broadest possible interpretation within the terms of the following claims.

What is claimed is:

l. A latching device for releasably maintaining a linearly movable switching device operator in an operated position. said latching device comprising: a housing having a rear end mountable on a front end of the switching'device. a latching lever having a latching surface movable between a released and a latching position in the housing. a spring biasing the latching lever and the latching surface toward the latching position. a latching assembly including: a movable plunger having a rear end engaging a front end of the operator and front end extending through an opening in a front end of the housing. a spring biasing the plunger toward the operator. a latch member movably mounted on the plunger providing a latching surface spaced between the ends of the plunger. adjustment means interconnecting the plunger and the latch member. said adjustment means including a constraining means for preventing relative movement between the latch member and the plunger when the plunger is moved by the spring and permitting relative movement between the latch member and plunger when a manual force applied to the front end of the plunger causes the operator to move to the operated position and the latching surface on the latch member to move to a position where it is engaged by the latching surface on the latching lever when the latching lever is at the latching position.

2. The device as recited in claim 1 including reset means engageable with the constraining means for permitting movement between the latch member and plunger when the latching device is detached from the switching device and a manual force is applied to the rear end of the plunger.

3. The device as recited in claim 1 including an electromagnet having an armature connected to the latch lever for moving the latch lever to its released position when the electromagnet is energized.

4. The device as recited in claim 3 wherein the constraining means is a pivotal member having an opening therein which receives the plunger and the adjustment means includes a spring surrounding the plunger and reacting between the pivotal member and latch memher.

5. The device as recited in claim 4 wherein the reset means includes a member having an end engaging the front wall of the housing and an end engaging the pivotal member causing the pivotal member to pivot against the force of the spring when the manual force is applied to the rear end of the plunger.

6. The device as recited in claim 1 wherein the latch member is movable in a guideway in the housing and guides the movement of the plunger in the housing.

7. The device as recited in claim 1 wherein the latch lever is pivotally mounted in the housing and includes a portion extending through an opening in the front end of the housing so the latch lever may be pivoted to the released position by a manual force applied to the extending portion.

8. The device as recited in claim 1 wherein the rear end of the plunger is provided by a cylindrical metal part and the front end is provided by an insulating part.

9. The device as recited in claim 4 wherein the adjustment means is mounted on the latch lever and includes a member having a slot therein which provides the pivot for the pivotal member.

10. The device as recited in claim 5 wherein the 35 housing includes a portion that is engaged by the latch member when a manual force is applied to the front end of the plunger.

11. A latching device for releasably maintaining a movable operator of a switch in an operated position,

said latching device comprising: a housing having an end mountable on an end of the switch. a plunger axially movable in the housing and having a first end engaging the operator and a second end accessible through an opening in the housing. a latch member movable on the plunger and having a latch surface spaced intermediate the ends of the plunger. a latch lever movable in the housing between a released and a latching position and presenting a latching surface at a predetermined position in the housing when the latch lever is at the latching position. and adjustment means releasably maintaining the position of the latch member on the plunger so the latch surface on the latch member is engaged by the latch surface on the latch lever when the latch lever is at the latching position and the operator is at the operated position. said adjustment means including constraining means having a portion engaging the plunger for preventing movement of the latch member on the plunger when the plunger moves in response to operator movement and permitting movement of the latch member on the plunger when a manual force applied to the second end causes the operator to move to the operated position.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. I 3,882,435

|NVENTOR(5) 1 W.E. Grass and W.C. Karch It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Claim 5, change "4" to --2-.

Signed and Scaled this Sixteenth D y 0' May 1978 RUI'H (I MASON LUTRELLl-I l-'. PARKER Arresting (If/Iver Acting Commissioner of Parents and Trademarks UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. I 3,882,435 6 DATED May 6, 1975 |NVENT0R(5 1 W.E. Grass and W.C. Karch It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Claim 5, change "4" to 2.

Signed and Scaled this i Sixteenth D r y I 1 sr:,-\|. t

Arum: Q RUTH MASON LU'I'Rl-ILLl-I F. PARKER g A Hosting ()flicvr Acting ('ommisxiom'r of Patents and Trademarks a; a t

r o; t r I r i t Q 

1. A latching device for releasably maintaining a linearly movable switching device operator in an operated position, said latching device comprising: a housing having a rear end mountable on a front end of the switching device, a latching lever having a latching surface movable between a released and a latching position in the housing, a spring biasing the latching lever and the latching surface toward the latching position, a latching assembly including: a movable plunger having a rear end engaging a front end of the operator and front end extending through an opening in a front end of the housing, a spring biasing the plunger toward the operator, a latch member movably mounted on the plunger providing a latching surface spaced between the ends of the plunger, adjustment means interconnecting the plunger and the latch member, said adjustment means including a constraining means for preventing relative movement between the latch member and the plunger when the plunger is moved by the spring and permitting relative movement between the latch member and plunger when a manual force applied to the front end of the plunger causes the operator to move to the operated position and the latching surface on the latch member to move to a position where it is engaged by the latching surface on the latching lever when the latching lever is at the latching position.
 2. The device as recited in claim 1 including reset means engageable with the constraining means for permitting movement between the latch member and plunger when the latching device is detached from the switching device and a manual force is applied to the rear end of the plunger.
 3. The device as recited in claim 1 including an electromagnet having an armature connected to the latch lever for moving The latch lever to its released position when the electromagnet is energized.
 4. The device as recited in claim 3 wherein the constraining means is a pivotal member having an opening therein which receives the plunger and the adjustment means includes a spring surrounding the plunger and reacting between the pivotal member and latch member.
 5. The device as recited in claim 4 wherein the reset means includes a member having an end engaging the front wall of the housing and an end engaging the pivotal member causing the pivotal member to pivot against the force of the spring when the manual force is applied to the rear end of the plunger.
 6. The device as recited in claim 1 wherein the latch member is movable in a guideway in the housing and guides the movement of the plunger in the housing.
 7. The device as recited in claim 1 wherein the latch lever is pivotally mounted in the housing and includes a portion extending through an opening in the front end of the housing so the latch lever may be pivoted to the released position by a manual force applied to the extending portion.
 8. The device as recited in claim 1 wherein the rear end of the plunger is provided by a cylindrical metal part and the front end is provided by an insulating part.
 9. The device as recited in claim 4 wherein the adjustment means is mounted on the latch lever and includes a member having a slot therein which provides the pivot for the pivotal member.
 10. The device as recited in claim 5 wherein the housing includes a portion that is engaged by the latch member when a manual force is applied to the front end of the plunger.
 11. A latching device for releasably maintaining a movable operator of a switch in an operated position, said latching device comprising: a housing having an end mountable on an end of the switch, a plunger axially movable in the housing and having a first end engaging the operator and a second end accessible through an opening in the housing, a latch member movable on the plunger and having a latch surface spaced intermediate the ends of the plunger, a latch lever movable in the housing between a released and a latching position and presenting a latching surface at a predetermined position in the housing when the latch lever is at the latching position, and adjustment means releasably maintaining the position of the latch member on the plunger so the latch surface on the latch member is engaged by the latch surface on the latch lever when the latch lever is at the latching position and the operator is at the operated position, said adjustment means including constraining means having a portion engaging the plunger for preventing movement of the latch member on the plunger when the plunger moves in response to operator movement and permitting movement of the latch member on the plunger when a manual force applied to the second end causes the operator to move to the operated position. 